(1) Field of the Invention
The present invention relates to a coating composition for use in hydrophilic treatment, a hydrophilic-treating method and hydrophilically treated heat exchanger fins.
(2) Description of the Prior Art
The condensate developed during air-cooling by the air conditioning equipment forms water drops, which then form water bridges between the heat exchanger fins to narrow the pathway of the air to flow through between the heat exchanger fins, resulting in increasing a airing resistance to produce problems such as loss of electric power, generation of noises, scattering of water drops, and the like. As a means to prevent such phenomena, it has been practiced to impart hydrophilic properties on the surface of the aluminium heat exchanger fins (hereinafter may simply be referred to as fins) so as to prevent the water drops and water bridges from being formed.
The method of effecting the hydrophilic treatment on the surface of the heat exchanger fins may include the following two methods, that is, 1 the so-called after-coat method which comprises subjecting an aluminium plate to fabrication to form fins, followed by assembling the fins, and coating a surface treating agent onto the surface of the fins by the coating means such as dip coating, spray coating, shower coating and the like; and 2 the so-called pre-coat method which comprises coating a surface treating agent onto an aluminium plate by a roll coater or the like beforehand to form a surface treated film, followed by subjecting the surface treated aluminium plate to press molding and fabrication to form fins.
Examples of the method, which has practically been used according to the method of imparting hydrophilic properties on the surface of the fins, as in the above method 1, may include (1) a method of coating a water-glass represented by the general formula: mSiO.sub.2 /nNa.sub.2 O (see, for example, Japanese Patent Application Laid-Open No. 13078/84); (2) a method of coating a solution containing, as a major component, an organic polymer resin such as water-soluble polyamide resin to form a resin film (see, for example, Japanese Patent Application Laid-Open No. 250495/86); and the like. Although the above methods have practically been used, the above methods are not satisfactory, but still has problems to be improved in durability of hydrophilic properties such as contact angle of water drops and overall water wetting properties for the treated plate, corrosion resistance, smell, press molding properties, and in stability of the treating solution. For example, in case of the method of using the water-glass in the above method (1) showing such a good hydrophilic durability that the contact to the water drop is 20.degree. or less, the resulting fins thus treated as above have such problems that the surface of the treating film shows powdery appearance with time, that the resulting powdery material is scattered during passage of air to develop cement smell or chemical smell, and that the water-glass is hydrolyzed by the condensate developed during the operation of the heat exchanger and the surface of the fins is alkalized, resulting in that pitting corrosion is likely to take place and in that the white powder of aluminium hydroxide as the corrosion product is scattered to produce a problem from the standpoint of environmental conservation.
Advancements in miniaturization and weight-saving have recently been made for the air conditioning equipment, and the heat exchanger, too, is of a compact design, resulting in that the space between fins is reduced, that higher hydrophilic properties are demanded, and that it is essential for the contact angle to water to be 30.degree. or less.
Further, since the comfortable housing space has recently been demanded, development of smell from the air conditioning equipment is becoming a problem to be solved. Japanese Patent Application Laid-Open Nos. 10051/83 and 168675/86 propose the use of a treating agent containing fungiproofing agent and mildewproofing agent as a measure against a coated film smell at the beginning of using the air conditioning equipment, an unpleasant smell developed within the air conditioning equipment due to microorganisms at the start of the operation, etc. with such unsatisfactory results that further improvements are demanded.
As above mentioned, the methods being practically used at present can not satisfactorily meet the above demands, and developments of a coating composition for use in hydrophilic treatment, a method of hydrophilic treatment and hydrophilically treated heat exchanger fins which are capable of providing improved hydrophilic properties and corrosion resistance and do not produce the problem of developing smell so as to meet the above demands.